1. Field of the Invention
The present invention relates to a planographic printing plate manufacturing apparatus, and more particularly, to a photosensitive planographic printing plate manufacturing apparatus.
2. Description of the Related Art
In the engraving method (including the electronic photoengraving method) in recent years, planographic printing plates, such as a photosensitive printing plate and a heat sensitive printing plate, have been widely used in order to facilitate automation of a plate making process. The planographic printing plate is generally manufactured by such a way that a supporting body such as a sheet-like or coil-like aluminum plate is surface-treated by a separate process, such as for example, a graining process, an anodic oxidation process, a silicate process, an other chemical conversion process, or by properly combining these processes, and that the surface-treated supporting body is then coated with a photosensitive layer or a heat sensitive layer and dried, so as to thereafter be cut into a desired size. The manufactured planographic printing plate is subjected to plate making processes, such as an exposure process, a development process, and a gum coating process, and is set in a printing machine. Then, ink is applied to the planographic printing plate set in the printing machine. The applied ink is transferred from the planographic printing plate, so that characters, images and the like are printed on a paper surface.
Meanwhile, the planographic printing plate is manufactured through a cutting process for cutting a wide metallic web in the longitudinal direction. The cutting process is performed by such a way that paired upper and lower knives are provided, and the web is made to pass between the upper knife and the lower knife.
In the case of the metallic web, a rounded sag is formed on one cut surface, and a projecting burr is formed on the other cut surface. The web on which the burr is formed causes damage to the planographic printing plate used as a product. That is, in the manufacturing process, the products of planographic printing plates are stacked on a skid and directly set in a setter, and when the number of remaining planographic printing plates is reduced to be small, there is performed an operation in which the skid as a whole is exchanged, and the remaining planographic printing plates are stacked on the newly set skid. If the burr is present at this time, there occurs a trouble that the planographic printing plate is damaged by the projection of the burr.
On the other hand, in the case where the planographic printing plate is smaller than a printing paper, such as the case of a newspaper printing plate, the ink may adhere to the edge of the printing plate to cause a linear stain (also referred to as edge stain or frame stain). In order to suppress the edge stain, there is known a method in which the stress concentration of the printing roll is reduced by providing a round part in the edge on the side of the printing surface. To this end, the droop deformation obtained by the shearing is utilized.
However, the height of droop deformation and the projecting amount of the burr on the surface opposite the droop are correlated with each other. When the edge stain is intended to be prevented by increasing the droop height, there occurs a problem that the projecting amount of the burr is also increased, so as to thereby easily damage the printing plate. In order to solve the problem, a method in which the lower knife is formed at a predetermined inclination angle, is described in Japanese Patent Application Laid-Open No. 7-164235, Japanese Patent Application Laid-Open No. 2000-61724 and in FIG. 3 of Japanese Patent Application Laid-Open No. 2001-18546. However, in the former method, when the angle of the lower knife is made small to thoroughly suppress the burr from projecting from the web lower surface, a burr is formed by a raised part newly formed on the web lower surface. The newly formed burr may cause damage to the products when the products are stacked.
Further, in FIG. 6 and the description of Japanese Patent Application Laid-Open No. 2001-18546, there is described a method in which a level difference is provided by making the diameter at the cutting position of the lower knife smaller than the diameter of the receiving part.